I don't know the math or algorithms behind the synther, so PS people can tell about this theory: it IS a problem of not having enough photos. For example:
If you rotate the building so you are looking down at the staircase and the 2nd floor hallway from the top, you'll see they don't align with the outer walls of the building and the tunnel. I don't have the building's blueprint, but I am guessing in reality, the staircase and the hallway align perfectly with the building walls. The reason they don't in the Point Cloud is that the synther does not have enough information.
In the Carter House synth, imagine if the steps are NOT fixed but are actually MOVABLE in real life. Then it's obvious how you can achieve the ghost effect.
It's like the ghost points from living or non-living things that move. If you have more photos to cover the steps, I think the 2 ghosts will merge and the effect gone.